Method and device at a single chamber air drier

ABSTRACT

For a single chamber air drier (SD) in a compressed air system on a vehicle the volume of dry regeneration air required to regenerate a desiccant in the air drier has to be determined. This can be accomplished in that data regarding system pressure (p), outdoor temperature (T) and supplied air volume are continuously provided to a computer (ECU), which in relation to these parameters controls the supply of regeneration air to the air drier.

[0001] This application is a continuation of pending InternationalApplication No. PCT/SE00/00588 filed Mar. 24, 2000, designating theUnited States and claiming priority of Swedish Application No. 9901071-2filed Mar. 24, 1999.

TECHNICAL FIELD

[0002] The present invention relates to a method and device at a singlechamber air drier in a compressed air system for determining the volumeof dry regeneration air required to regenerate a desiccant in the airdrier.

BACKGROUND OF THE INVENTION

[0003] A compressed air system for a vehicle, normally a truck or bus,usually includes an air drier for removing moisture from the air, as themoisture can be detrimental for air consumers in the vehicle, such asbrakes, air suspensions, and door openers.

[0004] The supplied volume of air in the compressed air system variesdepending on the driving conditions and the vehicle type.

[0005] Climate conditions also vary considerably and thus the moisturecontent of the air, which directly influences the air drier.

[0006] Further, the compressed air is often contaminated in thecompressor by its lubricant, which partly joins the air flow into thecompressed air system and gradually deteriorates the desiccant in theair drier.

[0007] The conventional way to regenerate the desiccant in a singlechamber air drier is to supply a constant volume of dried air from thesystem, either via a special regeneration tank or via a regenerationvalve opening for a fixed time period.

[0008] This method implies that the volume of regeneration air has to beover-dimensioned in order to manage the few worst loads on the desiccantwith regard to throughput air volume and the moisture content of theair.

[0009] The contamination of the desiccant gradually decreases thecapacity, so that the drying effect gradually disappears in spite ofsufficient regeneration capacity.

[0010] The Invention

[0011] In a method according to the invention the determination of therequired volume of dry regeneration air is achieved in that dataregarding system pressure, outdoor temperature and supplied air volumeare continuously provided to a computer, which in relation to theseparameters controls the supply of regeneration air to the air drier.

[0012] A device for carrying out this method has a computer forcontrolling two solenoids at the air drier, wherein the first solenoidprovides a pilot signal to an unloader valve of the air drier and thesecond solenoid—subordinated to the first solenoid valve—controls thevolume of regeneration air supplied to the air drier and wherein thecomputer is arranged to continuously receive data regarding systempressure, outdoor temperature and supplied air volume.

[0013] By substituting the conventional mechanical/pneumatical valves inthe air drier and sometimes the regeneration tank for two solenoidvalves controlled via an onboard computer, a variable volume ofregeneration air can be produced and the influence on the dryingfunction of the system pressure, the temperature, and contaminations canbe taken into account for the purpose of making the use of theregeneration air more effective, which leads to an improved dryingfunction, energy saving, lower maintenance, and lower installationcosts.

[0014] If the air drier has a large capacity, the new control makes itpossible to determine the conditions for optimizing the use of thevehicle. This means that the calculated need for regeneration air can bestored in a memory, so that the balance in the air drier can be restoredat a suitable time. The normal pressure span can be varied for varyingthe number of drainages and regenerations, and the wear of the desiccantcan be taken into account.

[0015] A diagnosis system can also be provided, which gives informationwhen a serious system failure occurs or when the compressed airconsumption goes outside limits where dry air can be guaranteed.

THE DRAWING

[0016] In the enclosed drawing a very schematic view of a deviceaccording to the invention is shown.

DETAILED DESCRIPTION OF EMBODIMENTS

[0017] It is well known in the art that compressed air to be used forexample for an air brake system in a road vehicle, primarily a truck orbus, should be dried before use. This may be accomplished by means of anair drier installed in the system between an air compressor and an airconsumer or a tank for dried air.

[0018] Air to be dried is transferred from the compressor through adesiccant (and possibly one or more filters) in the air drier. After acertain service time the desiccant has become moist and has to beregenerated or dried in order to be able to continue its dryingfunction. This regeneration is performed by means of dried air from thesystem. The present invention is concerned with the control of thisregeneration.

[0019] In the FIGURE a single chamber air drier SD is schematicallydepicted. The compressed air system in which this air drier isincorporated is conventional and will not be further described. Theregeneration of the air drier SD is controlled by an on-board computerECU over two solenoids S1 and S2. The first solenoid S1 provides a pilotsignal to a conventional unloader valve of the air drier SD for controlof a compressed air signal to the compressor or its clutch. The secondsolenoid S2 controls the volume of regeneration air supplied to the airdrier and is subordinated to the first solenoid S1.

[0020] Continuous information about outdoor temperature T (in ° C.),system pressure p (in bar), time t (in s), and number of engine orrather compressor revolutions is supplied to the computer ECU.

[0021] If the air intake to the compressor is placed after a turbocharger, supplying i a the engine with air, information about the turbopressure may also be supplied to the computer ECU, because the air flowis dependent on the air consumption of the engine.

[0022] Data specific for the vehicle are also supplied to the computerECU. Such data include certain pressure levels, compressor data, andlimits for compressor revolution numbers. These data are preferably onlysupplied once.

[0023] During the lifetime of the vehicle also supplemental data may besupplied to the computer ECU, for example at servicing the vehicle,which may lead to a change of an adjustment factor in the computer, forexample if the vehicle is not operated in the precontemplated way.

[0024] Additionally, it may be possible to supply to the computer ECUinformation about speed, fuel supply and the like, so that theutilization of the vehicle becomes optimal.

[0025] From the computer ECU a diagnosis signal to other means in thevehicle may be provided, for example regarding system failures, leakageand so forth. In certain cases the diagnosis signal may lead to avisible or audible signal to the driver of the vehicle.

[0026] A function for forced regeneration and a function foraccumulating incomplete regenerations provide a guarantee for perfectlysatisfactory function. A prerequisite for maximum accumulation ofregeneration time has been determined.

[0027] The following abbreviations are used:

[0028] p=continuously measured variable system pressure (bar)

[0029] p1=maximum working pressure (bar)

[0030] p2=variable cut-in pressure (bar)

[0031] p3=nominal cut-in pressure (bar)

[0032] aO=atmospheric pressure (normally 1 atm)

[0033] at=turbo pressure (atm)

[0034] t1=time for S2 (s)

[0035] tpott=accumulated, not spent, historical regeneration time (s)

[0036] N1=number of compressor revolutions before forced regeneration

[0037] N2=number of covered compressor revolutions

[0038] N3=accumulated number of covered compressor revolutions

[0039] Nnom=predetermined number of compressor revolutions beforedesiccant exchange

[0040] U=constant for compressor capacity (1/rev)

[0041] T=outdoor temperature (° C.)

[0042] W=adjustment factor, normally=1

[0043] The time for activating S2 is determined in the following way:

t1=f(p, N2, U, T, W)+tpott

[0044] The variable cut-in pressure is determined in the following way:

p2=f(p3, T, N3, Nnom)

[0045] The number of revolutions to forced regeneration is determined inthe following way:

N1=f(p1, T, U)

[0046] When N3=Nnom a warning signal is issued.

[0047] Presently, the following practical relations may be used:

t1=Vreg/Qreg×C×W+tpott

[0048] where Vreg stands for a theoretical need of regeneration air inrelation to the volume of dried compressed air Vreg = at/aO × N2 ×U/(p + 1); Qreg = 8.5 × p/60; C = 1 + 0.02T; W = 1 (normally) p2 = p3 +p4 + p5 where: p4 = 0.025T (temperature compensation) p5 = 0.1 × N3/Nnom(ageing factor) p1 − 2.5 < p2 < p1 − 0.8 (limitations) N1 = 1/U × Qreg ×(p + 1) × 20 × C Qreg × (p + 1) × 20 = maximum volume during maximumnormal load cycle of 20 s of undried air from the compressor.

1. A method at a single chamber air drier (SD) in a compressed airsystem for determining the volume of dry regeneration air required toregenerate a desiccant in the air drier, characterized in that dataregarding system pressure (p), outdoor temperature (T) and supplied airvolume are continuously provided to a computer (ECU), which in relationto these parameters controls the supply of regeneration air to the airdrier (SD).
 2. A method according to claim 1, characterized in that theregeneration time is determined as a function of the system pressure(p), of the outdoor temperature (T), of the volume of air supplied bythe compressor and of a constant adjustment factor plus an accumulatedhistorical regeneration time.
 3. A method according to claim 2,characterized in that the volume of air supplied by the compressor isthe number of compressor revolutions times the compressor capacityexpressed in volume/revolution.
 4. A method according to claim 1,characterized in that a variable cut-in pressure is determined as afunction of a nominal cut-in pressure, of the outdoor temperature and ofthe ageing of the desiccant in the air drier.
 5. A method according toclaim 4, characterized in that the ageing of the desiccant is determinedby the accumulated number of compressor revolutions in relation to apredetermined number of compressor revolutions before desiccantexchange.
 6. A method according to claim 1, characterized in that thenumber of compressor revolutions before forced regeneration isdetermined as a function of maximum working pressure, of outdoortemperature and of compressor capacity in volume per revolution.
 7. Adevice for carrying out the method of claim 1, characterized by acomputer (ECU) for controlling two solenoids (S1, S2) at the air drier(SD), wherein the first solenoid (S1) provides a pilot signal to anunloader valve of the air drier and the second solenoid(S2)—subordinated to the first solenoid valve—controls the volume ofregeneration air supplied to the air drier and wherein the computer isarranged to continuously receive data regarding system pressure (p),outdoor temperature (T) and supplied air volume.